Make sure you got a Map then
The overnight camping is not allowed over there but mose of campers are parking everywhere so you would need to check with the local info site or DOC before you begin your trip.
There will be signs showing, so it's only not allowed where you see signs that it is not allowed, and in National Parks outside official campsites.
You can then for example park at "Top 10 Holiday Park", pricing is approx $80-100 per night for this kind of park motels.
Please keep in mind your safety, and park well off the road.